A microscope has been widely used to measure physical properties, and the like, of various measurement objects. For example, infrared spectra of a measurement object can be measured by using a microscope, so that components, and the like, of a specific minute area of the measurement object can be measured on the basis of the characteristics of the infrared spectra.
Meanwhile, in order to obtain optical data of the measurement object in this way, it is necessary to collect a light beam reflected from the measurement object or a light beam transmitted through the measurement object.
However, the method of collecting a light beam reflected from or transmitted through a measurement object is extremely difficult to be applied to such as the analysis of the surface of a material of a polymer membrane, a semiconductor, and the like, or the analysis of a material exhibiting very strong light absorption characteristics, such as, for example, a solute in an aqueous solution whose infrared spectra have been difficult to be measured.
Thus, a total reflection measuring method is applied to a measurement object to which the above described general method of measuring a reflected or transmitted light beam is difficult to be applied.
In the total reflection measuring method, an ATR hemispherical prism or an ATR triangle pole prism, which has a larger refractive index n1 than a refractive index n2 of a measurement object, is mounted on the measurement object so as to make a luminous flux having a wavelength λ incident on the prism from the outside.
Then, when the incident angle θ from the prism to the measurement object is set larger than the critical angle θc, the incident light beam is totally reflected on the critical surface between the measurement object and the prism, but at the reflection point, a slight part of the luminous flux penetrates into the measurement object. When the penetration depth dp of the light beam is defined by the depth at which the light intensity is reduced to 1/e, and when the wavelength of the light beam is λ, the penetration depth dp is expressed by the following expression 1.dp=λ/[2πn1{(sin2θ−(n2/n1)2}1/2]  Expression 1
Therefore, when the light beam is absorbed by the measurement object, the amount of the light beam totally reflected on the critical surface is reduced by the absorbed amount. By analyzing the characteristics of the light beam totally reflected on the critical surface between the measurement object and the prism, it is possible to obtain the optical information from the measurement object, even in the case where the surface of a polymer membrane, a semiconductor, and the like, is analyzed, or where the measurement object exhibits very strong light absorption characteristics.
However, in the case where the conventional total reflection measuring apparatus is applied to a general microscopic measuring apparatus, the surface state of the measurement object cannot be grasped even by visually observing the totally reflected light beam. Thus, it is necessary that, after the measurement area on the measurement object is visually observed by visible light in the state where the prismis retreated from the optical path, the prism is returned to the optical path so as to optically obtain the information. Therefore, the operation is complicated and also there is a limit in the improvement of the measurement accuracy.    Patent literature 1: Japanese published unexamined application No. 07-12717